The invention relates to a method for managing an apparatus for treating blood outside a body. It also relates to a system implementing this method.
The invention relates more particularly to a method for managing an apparatus for treating blood outside a body with a view to removing liquid and solutes present in the blood. Such a method is more commonly called haemodialysis.
At present, several types of haemodialysis are known, carried out with apparatuses, called dialysis generators, comprising a filter, called a dialyzer, in which an exchange of solutes and liquids is carried out through a semi-permeable membrane.
In so-called “pure ultrafiltration” methods, the liquid to be removed is taken from the blood by pressure gradient and the solutes to be removed are transported by convection with the liquid.
In other haemodialysis methods, a fluid of a predetermined composition is introduced into the non-blood compartment of the dialyzer. The removal of the liquids from the blood through the semi-permeable membrane occurs by pressure gradient. The exchange of solutes through the membrane is achieved mainly by diffusion due to the concentration gradient of the solutes. Depending on the pressures and the porosity of the membrane various exchanges of water and solutes can take place.
In haemodiafiltration, the exchanges of solutes take place by diffusion and by convection. An additional quantity of liquid is removed by ultrafiltration. A substitution liquid is infused into the blood to compensate for the additional quantity of liquid removed.
All these types of haemodialysis allow the removal of an excess of liquid from the blood treated. The total quantity of liquid removed from the start to the end of the treatment (weight loss) is one of the most important parameters in the treatment, and it is generally fixed at the start of the treatment as a target.
Another important parameter is the total treatment time. The quantity of liquid removed from the blood treated per unit of time is known by the name of weight loss rate. Generally, the weight loss rate is fixed at a constant value or a predefined profile.
In haemodiafiltration, the quantity of liquid infused per unit of time is the infusion rate. The ultrafiltration rate is determined as the sum of the weight loss rate and the infusion rate. The difference in pressure on either side of the membrane is called the transmembrane pressure (PTM).
The ratio of the hourly ultrafiltration rate to the transmembrane pressure is called the ultrafiltration coefficient (KUF).
The manufacturers of treatment apparatuses give, for each type of dialyzer, an ultrafiltration coefficient value (KUF) measured in vitro with standard bovine blood. This value is generally taken as a constant in vivo. In vivo, for a given ultrafiltration flow rate (QINF), the adsorption into the membrane of proteins modifies the convection resistance and hence the transmembrane pressure (PTM). The ultrafiltration coefficient (KUF=QINF/PTM) is therefore not constant. It varies with the characteristics of the blood. The composition of the blood can vary during a session or be modified over several sessions. If the total ultrafiltered flow rate is greatly increased, as is the case in haemodiafiltration, the transmembrane pressure increases. A maximum flow rate value can be reached. This is the plateau where an increase in the transmembrane pressure (PTM) does not result in an increase in flow rate (dQuf/dPTM=0).
This maximum value of the total ultrafiltered flow rate is generally sought as a target value where convection resistance is significant. The weight loss results in an increase in the haematocrit during a session which can lead to haemoconcentration and the saturation of the membrane by proteins, resulting in transmembrane pressure alarms. The removal of toxins, in particular of high molecular weight, under these conditions diminishes. As the PTM increases, the ultrafiltration coefficient (KUF) decreases.
A purpose of the invention is to remedy these drawbacks.
Another purpose of the invention is to propose a method for managing an apparatus for treating blood outside a body making it possible to improve the operation and the yield of the treatment apparatus.
Another purpose of the invention is to provide an apparatus for treating blood outside a body having a better yield than the apparatuses known at present.